Was it really a "feature"? They put two big fuck off engines in a tight airframe designed to do >M2 wet, it's not that surprising that it could do >M1 dry. Bear in mind that modern fighter engines are turbofans, so they gain much more from afterburn than the relatively primitive non-by-pass Avon, e.g. about +30% for the Avon vs. +50% for the P&W F119 in the F-22.
Was it really a "feature"? They put two big fuck off engines in a tight airframe designed to do >M2 wet, it's not that surprising that it could do >M1 dry. Bear in mind that modern fighter engines are turbofans, so they gain much more from afterburn than the relatively primitive non-by-pass Avon, e.g. about +30% for the Avon vs. +50% for the P&W F119 in the F-22.